The invention relates to metal-oxide-metal-oxide-metal, MOMOM, devices and fabrication methods.
In an MOMOM device, current is conducted by the tunneling of carriers such as electrons through the oxide barriers between the metal layers. Tunneling probability is determined by various factors, including the excitation level of the carriers, the work function and the height of the barrier between the metal and the oxide, the thickness of the oxide, etc. The MOMOM structure is analogous to a bipolar transistor, and it is desirable to have a very thin middle metal base region so that carriers surmounting the first oxide barrier from the end emitter metal will coast through the base metal layer and be collected in the end collector metal layer. It is also desirable to provide independently variable work function barrier heights and oxide thicknesses for the emitter-base junction and the base-collector junction. This enables differing input and output impedance values.
The present invention provides structural geometry and simplified efficient processing fabrication of a vertically layered MOMOM device satisfying the above desirable characteristics and capable of operation in the visible region. Extremely small junction areas are provided, for example 10.sup.-10 cm.sup.2, capable of detecting signals in the visible wavelength region, i.e., optical frequencies can excite the carriers to cross the junction barriers.